Inkjet printers eject ink droplets from a nozzle of an ink jet head. Ink jet heads use various methods of discharging ink, including the use of a piezoelectric element. An inkjet head using a piezoelectric element discharges ink when a driving signal is applied to the piezoelectric element so as to deform the piezoelectric element. For a reduction of power consumption or the like, it is desired that only a low voltage of the driving signal (hereinafter, referred to as “driving voltage”) is required.